Process of evaluating corrosion resistance

ABSTRACT

The present invention is directed to a process for evaluating corrosion resistance of coated metals substrates, such as autobodies at an accelerated rate. An anode and cathode coated with protective coating being tested are exposed to an electrolyte in a chamber of a corrosion resistance evaluator. These coatings are provided with predetermined and standardized defects, such as micro-holes to accelerate the corrosion of the underlying metal substrate in a predictable and repeatable manner. The coated cathode/anode pair is subject to a start-up period followed by series preset DC voltages modulated in triangular, truncated triangular or trapezoidal manner for preset durations that are interspaced with recovery periods. The impedance data collected are then used to arrive at the corrosion performance resistance of the coating applied over the cathode/anode pair. The foregoing evaluator substantially reduces the time required to test corrosion from several days (40 plus days) to few days (about two days).

FIELD OF INVENTION

The present invention is directed to a process for evaluating thecorrosion resistance of multi-coated and single coated metal substratesand more particularly directed to a corrosion resistance evaluator andto a process used therein for evaluating the corrosion resistance ofmulti-coated and single coated metal substrates at an accelerated rate.

BACKGROUND OF INVENTION

Currently, no short term (less than 2 days) test method exists toevaluate the long-term corrosion protection afforded by a protectivecoating from a coating composition, such as automotive OEM or automotiverefinish coating compositions, applied over a metal substrate, such asautomotive body. The current standard test methods rely primarily onenvironmental chamber exposure, followed by visual and mechanicaltesting of the metal with its protective coating. This kind of testingis long (up to 40 days or more exposure time), subjective, highlydependent on the exposure geometry, and on the person doing theevaluation. Consequently, these methods are not very reproducible. Thecorrosion resistance data is qualitative, and therefore the relativeperformance of an acceptable coating cannot be easily determined. Anynew test method must correlate well with the traditional, the accepted,standard environmental chamber test methods, must be reproducible, andmust supply a qualitative and quantitative ranking of the unknowndirect-to-metal (DTM) corrosion resistant coating.

The experimental corrosion test methods have been reported for reducingthe test duration. These methods primarily utilize electrochemicalimpedance spectroscopy (EIS) or AC impedance technology. Since these ACimpedance based methods typically only offer a more sensitive tool fordetecting corrosion at an early stage of exposure time, the corrosionprocess itself is not accelerated by these methods. Therefore, thesemethods still require relatively long exposure times before themeaningful data can be obtained. The length of time needed to getmeaningful corrosion data approaches that of the standard methods. Moreimportantly, the corrosion resistance data obtained by these methods,particularly during the initial exposure time, are primarily dictated bythe intrinsic defects of the coatings. These intrinsic defects generallyproduced during the preparation of coated samples are not necessarilyrelated to the actual performance of the coatings. Misleadinginformation could be obtained if the data are not analyzed correctly.Consequently, the standard convention methods are still favored.Therefore, a need still exists for a device and a process that not onlyaccelerates the corrosion of protectively coated metal substrates butalso mimics the corrosion typically seen in working environments, suchas those experienced by bodies of automobiles during use.

STATEMENT OF INVENTION

The present invention is directed to a process for evaluating corrosionresistance of an anode coating applied over a surface of an anode andcorrosion resistance of a cathode coating applied over a surface of acathode comprising:

(i) sealably positioning said anode in an anode holder located on achamber of a corrosion resistance evaluator, said chamber containing anelectrolyte therein such that a portion of said anode coating is exposedto said electrolyte, said portion of said anode coating having an anodedefect thereon;

(ii) sealably positioning said cathode in a cathode holder located onsaid chamber such that a portion of said cathode coating is exposed tosaid electrolyte, said portion of said cathode coating having a cathodedefect thereon;

(iii) directing a computer of said evaluator through computer readableprogram code means residing on a usable storage medium located in saidcomputer and configured to cause said computer to perform followingsteps comprising:

-   -   (a) subjecting said portions of said anode coating and said        cathode coating to a start-up period;    -   (b) directing an impedance measurement device in communication        with said computer and is connected to said cathode and said        anode to measure an impedance A during said start-up period at        preset intervals to produce n1 set of said impedances A measured        at preset frequencies ranging from 100000 to 10⁻⁶ Hz of AC power        with an amplitude ranging from 10 to 50 mV supplied by an        alternating current variable power generator in communication        with said computer, said alternating current variable power        generator having AC output leads that connect to said cathode        and anode;    -   (c) generating A impedance Nyquist plot for each said impedance        A in said n1 set;    -   (d) determining start-up solution resistances (^(Sta)R_(sol.n1))        by:        -   1. measuring a distance between zero point on X-axis of said            A impedance Nyquist plot and a point on said X-axis of said            A impedance Nyquist plot where an impedance curve or an            extrapolated impedance curve directed to high start-up            solution frequencies in said A impedance Nyquist plot            intersects said X-axis to obtain real part of said impedance            A at said high start-up solution frequencies; and        -   2. repeating said step (d) (1) for each said impedance A in            said n1 set;    -   (e) determining start-up resistances (^(Sta)R_(Sta.n1)) by:        -   1. measuring a distance between zero point on X-axis of said            A impedance Nyquist plot and a point on said X-axis of said            A impedance Nyquist plot where an impedance curve or an            extrapolated impedance curve directed to low start-up            resistance frequencies in said A impedance Nyquist plot            intersects said X-axis to obtain real part of said impedance            A at said low start-up resistance frequencies; and        -   2. repeating said step (e) (1) for each said impedance A in            said n1 set;    -   (f) directing a direct current variable power generator to apply        V1 preset DC voltages in a triangular, truncated triangular or        trapezoidal manner for T1 preset durations, wherein said direct        current measurement device in communication with said computer        and connected to said cathode and said anode is used to measure        said preset DC voltages and wherein said V1 preset DC voltage        ranges from 0.1 millivolts to 10 volts and said T1 preset        duration ranges from half an hour to 100 hours;    -   (g) directing said impedance measurement device to measure an        impedance B at the end of each of said preset duration at said        preset frequencies of AC power supplied by said alternating        current variable power generator to produce n2 set of said        impedances B;    -   (h) generating B impedance Nyquist plot for each said impedance        B in said n2 set;    -   (i) determining triangular, truncated triangular or trapezoidal        solution resistances (^(Tra)R_(sol.n2)) by:        -   1. measuring a distance between zero point on X-axis of said            B impedance Nyquist plot and a point on said X-axis of said            B impedance Nyquist plot where an impedance curve or an            extrapolated impedance curve directed to high triangular,            truncated triangular or trapezoidal solution frequencies in            said B impedance Nyquist plot intersects said X-axis to            obtain real part of said impedance B at said high            triangular, truncated triangular or trapezoidal solution            frequencies;        -   2. repeating said step (i) (1) for each said impedance B in            said n2 set;    -   (j) determining triangular, truncated triangular or trapezoidal        resistances (^(Tra)R_(Tra.n2)) by:        -   1. measuring a distance between zero point on X-axis of said            B impedance Nyquist plot and a point on said X-axis of said            B impedance Nyquist plot where an impedance curve or an            extrapolated impedance curve directed to low triangular,            truncated triangular or trapezoidal resistance frequencies            in said B impedance Nyquist plot intersects said X-axis to            obtain real part of said impedance B at said low triangular,            truncated triangular or trapezoidal resistance frequencies;            and        -   2. repeating said step (j) (1) for each said impedance B in            said n2 set;    -   (k) subjecting said portions of said anode coating and said        cathode coating to T2 preset recovery periods in between each of        said T1 preset durations;    -   (l) directing said impedance measurement device to measure an        impedance C at the end of each of said T2 preset recovery        periods at said preset frequencies of AC power supplied by said        alternating current variable power generator to produce n3 set        of said impedances C;    -   (m) generating C impedance Nyquist plot for each said impedance        C in said n3 set;    -   (n) determining recovery solution resistances (^(Rec)R_(sol.n3))        by:        -   1. measuring a distance between zero point on X-axis of said            C impedance Nyquist plot and a point on said X-axis of said            C impedance Nyquist plot where an impedance curve or an            extrapolated impedance curve directed to high recovery            solution frequencies in said C impedance Nyquist plot            intersects said X-axis to obtain real part of said impedance            C at said high recovery solution frequencies;        -   2. repeating said step (n) (1) for each said impedance C in            said n3 set;    -   (o) determining recovery resistances (^(Rec)R_(Rec.n3)) by:        -   1. measuring a distance between zero point on X-axis of said            C impedance Nyquist plot and a point on said X-axis of said            C impedance Nyquist plot where an impedance curve or an            extrapolated impedance curve directed to low recovery            resistance frequencies in said C impedance Nyquist plot            intersects said X-axis to obtain real part of said impedance            C at said low recovery resistance frequencies; and        -   2. repeating said step (o) (1) for each said impedance C in            said n3 set;    -   (p) calculating corrosion performance resistance (R_(perf)) of        said anode and said cathode pair by using the following        equation:

R _(perf)=[Σ^(Sta) f _(n1)(^(Sta) R _(Sta.n1)−^(Sta) R_(Sol.n1))]/n1+[Σ^(Tra) f _(n2)(^(Tra) R _(Tra.n2)−^(Tra) R_(Sol.n2))]/n2+[Σ^(Rec) f _(n3)(^(Rec) R _(Rec.n3)−^(Rec) R_(Sol.n3))]/n3,

-   -   wherein n1, n2, n3 and n3 range from 1 to 100; and ^(Sta)f_(n1),        ^(Tra)f_(n2), and ^(Rec)f_(n3) range from 0.0000001 to 1; and    -   (q) causing said computer to:        -   (q1) direct a computer monitor to display said corrosion            performance resistance (R_(perf));        -   (q2) direct a printer to print said corrosion performance            resistance (R_(perf));        -   (q3) transfer said corrosion performance resistance            (R_(perf)) to a remote computer or a remote database; or        -   (q4) a combination thereof.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 broadly illustrates the process of anodic metal dissolution thatoccurs at anode.

FIG. 2 broadly illustrates the process of delamination that occurs atcathode.

FIG. 3 illustrates a longitudinal cross-sectional view of one embodimentof the corrosion resistance evaluator of the present invention.

FIGS. 4A, 4B, 4C, 4D, 4E and 4F represent a flowchart of means forconfiguring computer readable program code means used in the device ofthe present invention illustrated in FIG. 3.

FIG. 5 A illustrates one of the typical triangular DC voltage waveformprotocols used in the process of the present invention.

FIG. 5 B illustrates one of the typical truncated triangular DC voltagewaveform protocols used in the process of the present invention.

FIG. 5 C illustrates one of the typical trapezoidal DC voltage waveformprotocols used in the process of the present invention.

FIGS. 6 and 7 illustrate the deliberately created artificial defects onanode and cathode coatings for exposing the underlying surface of metalanodes and cathodes.

FIG. 8 illustrates a plan view of yet another embodiment of the presentinvention that provides for multiple chambers.

FIG. 9 illustrates a plan view of yet another embodiment of the presentinvention that provides for expeditious escape of gases generated duringthe corrosion testing process.

FIG. 10 illustrates A impedance Nyquist plot for impedance A obtained onE-coat H during start up period.

FIG. 11 illustrates the n1 set of the A impedance Nyquist plots of Aimpedances obtained.

FIG. 12 illustrates the expanded left part of the A impedance Nyquistplot of impedance A of FIG. 10 at high start-up solution frequencies.

FIG. 13 illustrates the expanded right part of the A impedance Nyquistplot of impedance A of FIG. 10 at low start-up resistance frequencies.

DETAILED DESCRIPTION OF PREFERRED THE EMBODIMENT

The evaluation of corrosion resistance of single layer or multilayerprotective coatings, such as those resulting from an automotive OEMpaint, an automotive refinish paint, a marine paint, an aircraft paint,an architectural paint, an industrial paint, a rubberized coating, apolytetrafluoroethylene coating, or a zinc-rich primer, typicallyapplied over metal substrates, such as steel, aluminum and copper, isvery important for determining the working life of a product, such as anautomobile, a ship or a crane.

When a metal substrate, such as an automobile body, is exposed toatmosphere, its surface is covered by a thin film of water produced bythe condensation of moisture in air, although it may not be visible dueto the extremely low thickness of the film. Many micro electrochemicalcorrosion cells can develop on the surface of metal substrate underneaththe water film due to the non-uniform properties of the metal substrate.Such non-uniformity can result from the differences in chemicalcomposition of the metal, differences in metal microstructure, or due tothe differences in mechanical stress of the surface of a metal. Suchnon-uniformity can lead to the formation of electrode potentialdifference on the surface.

It is believed that when the surface of metal is covered by theelectrolyte, such as water formed by the condensation of moisture, thelocations with a lower electrode potential turn into an anode while thelocations with a higher electrode potential turn into a cathode. Theseanodes and cathodes, covered with the electrolyte, can form many microelectrochemical corrosion cells across over the entire surface of metal,which in turn can produce corrosion. A workable corrosion cell isgenerally composed of three sub-processes—an anodic process, a cathodicprocess, and an electrolyte pathway to transfer ionic species. The anodeprocess in the corrosion is the metal that loses electrons to form itsionic species and thus can be dissolved into the electrolyte asillustrated in the following manner:

2Fe-4e(electron)=2Fe²⁺(ionic species)  1

When the condition is neutral, the cathode process in the corrosion isthe reduction of oxygen which gains the electrons released from theanode in the following manner:

O₂+2H₂O+4e(electron)=4OH⁻  2

This oxygen, required by the cathode process, generally comes from theoxygen dissolved in the water. In the electrolyte, such as water, Fe²⁺released from the anode transports towards cathode, and at the sametime, OH⁻ produced on the cathode transports toward anode. Eventually,they neutralize each other to keep the electrolyte at a neutralcondition. For a workable micro corrosion cell, the anode and cathodeprocess have to occur at the same time. The corrosion stops whenevereither of them is eliminated. For the corrosion of coated systems, asimilar corrosion mechanism occurs, but with some special featuresdescribed below.

Due to the coverage of metal surface by coating, it takes a long timefor the water to permeate through the coating thickness to approach theinterface of coating/metal substrate. Corrosion occurs only when thewater approaches the metal surface, or more specifically, the interfaceof coating/metal substrate. However, if the coating has defects, such asmicro-cracks, corrosion can be initiated immediately inside thesedefects. As a result, the corrosion data obtained by a conventional ACimpedance evaluation method, dictated or distorted by the intrinsicdefects of the coating, may not represent the actual true performance ofthe coating. As noted by the cathode reaction (in Equation 2 above), thepH of the cathode area is increased significantly when corrosion occurs.For many coating formulations, such an increased pH promotesdelamination of coating film from the metal substrate, which is one ofthe primary coating failure modes.

Under working conditions, these micro-anodes and micro-cathodes arerandomly distributed across the entire surface of metal substrate andthey are not distinguishable. However, in the device and process ofpresent invention, the anode and cathode are separated so that theseanodic and cathodic processes can be controlled and acceleratedindividually.

The preferred embodiment of this invention provide for:

An AC impedance method suitable for sensitively detecting any changecaused by the corrosion of metal substrate under the coating film;

A cathode separated from an anode in the device and process allows oneto respectively separately control and accelerate the corrosion processoccurring on the cathode and anode;

Artificial defects are provided on the anode and cathode so that theeffect of the intrinsic defects can be eliminated.

The present invention provides for a device and a process forcomprehensively evaluating the performance of coatings under variouscontrolled and accelerated conditions. In the start up period, theperformance of the coatings is evaluated under a natural condition. Inthe triangular, truncated triangular or trapezoidal period, theperformance of the coatings is evaluated at an accelerated condition. Inthis period, the anodic corrosion process at the anode site and thedelamination process on the cathode site are accelerated separately andgradually by means of sequentially triangular, truncated triangular ortrapezoidal DC voltages applied across the cathode and anode. Theinhibitive effect at the anode site, and the delamination resistance onthe cathode site are evaluated at the same time. In the recovery period,the recovery performances of the coatings are evaluated after stoppingthe severe corrosion that occurs when triangular, truncated triangularor trapezoidal DC voltages are applied across the cathode and anode.

FIGS. 1 and 2 illustrate the typical anodic dissolution process thatoccurs at an anode (FIG. 1) and the delamination processes that occur ata cathode (FIG. 2) of the present invention.

FIG. 1 illustrates the anodic end of the device of the present inventionof a typical multi-coating system applied over a metal substrate 110,FIG. 1 includes a dry conversion coating layer (phosphate layer) 112typically ranging in thickness from 2 to 50 nanometers applied over ametal substrate 110, followed by a dry layer of an electro-coated primer114 typically ranging in thickness from 25 to 250 micrometers, thenfollowed by a dry layer of either a basecoating or a sealer-basecoatingcombination 116 typically ranging in thickness from 20 to 50 micrometersfor the sealer, and 50 micrometers to 120 micrometers for thebasecoating (color coating). Typically, basecoating 116 is protectedwith a dry layer of a clearcoating 118 ranging in thickness from 30micrometers to 100 micrometers. A standardized defect is represented bya defect 120 that exposes metal substrate 110 to an electrolyte 122,such as 3% sodium chloride containing dissolved oxygen. If the metalsubstrate 110 is a cold rolled steel, ferrous ions are released in theelectrolyte and over time, the surface of substrate 110 corrodes to formpits 124, rust scales etc. Then the size of defect 120 may be increasedover time by corrosion, which then separates the multi-coating frommetal substrate 110 and corrodes and damages the underlying surface.

FIG. 2 illustrates the cathodic end of the device of the presentinvention. FIG. 2 shows a typical multi-coating applied over anautomobile metal body 210, which includes a dry layer of a conversioncoating 212 applied over metal substrate 210, followed by a dry layer ofan electro-coated primer 214 followed by a dry layer of a basecoating216 followed by a dry layer of a clearcoating 218, all havingthicknesses mentioned in the paragraph above. A standardized defect isrepresented by a defect 220 that exposes metal substrate 210 to anelectrolyte 222, such as 3% sodium chloride containing dissolved oxygen.When cathodic reactions occur, driven by the DC voltages applied, it isbelieved the pH at the cathode site will be increased due to thereduction of oxygen, and a higher pH will promote the delamination ofthe multi-coating from metal substrate 210 thereby further exposing theunderlying metal surface. In addition, hydrogen 224 is produced if theDC voltage applied is high enough, which can further promote adelamination process 226 (shown in FIG. 2) of the cathode by themechanical action from evolved hydrogen burbles.

Therefore, it is necessary to develop a testing device and processtherefor to expeditiously evaluate the corrosion resistance ofprotective coatings. One embodiment of a corrosion evaluator 1 for thepresent invention is shown in FIG. 3. Evaluator 1 includes a chamber 10,typically made of inert material, such as glass to retain an electrolyte12 therein. Chamber 10 is preferably cylindrical in shape. Some oftypical electrolytes can include an aqueous solution containing sodiumchloride at a concentration of three parts by weight based on 100 partsby weight of the aqueous solution, or an aqueous solution that simulatesacid rain or a corrosive chemical solution, such as those to whichmanufacturing equipment may be exposed to. Typically, the aqueoussolution containing sodium chloride is preferably used.

One end of chamber 10 is provided with a flanged opening 14 over whichan anode holder 16 can be mounted to retain an anode 18 made fromvarious types of steel, aluminum, and copper. Anode 18 is coated with ananode coating 20 made of a single layer or a multilayer protectivecoatings resulting from an automotive OEM paint, automotive refinishpaint, marine paint, aircraft paint, architectural paint, industrialpaint, rubberized coating, polytetrafluoroethylene coating, or zinc-richprimer. One approach to prevent leaking of electrolyte 12 can be toprovided an ‘O’ ring 22 retained in a circular groove on the flange ofopening 14, whereby anode holder 16 retains anode 18 against ‘O’ ring22. Anode holder 16 can be made of flexible material, such as rubber orit could be a clamp that grips anode 18. Anode coating 20 is providedwith an anode defect 24 that exposes the surface of anode 18 toelectrolyte 12.

A the other end of chamber 10 is provided with a flanged opening 26 overwhich a cathode holder 28 can be mounted to retain a cathode 30 madefrom various types of steel, aluminum, and copper. Cathode 30 is coatedwith a cathode coating 32 made of a single layer or a multilayerprotective coatings resulting from an automotive OEM paint, automotiverefinish paint, marine paint, aircraft paint, architectural paint,industrial paint, rubberized coating, polytetrafluoroethylene coating,or zinc-rich primer. One approach to prevent leaking of electrolyte 12can be to provide an ‘O’ ring 22 retained in a circular groove on theflange of opening 26, whereby cathode holder 28 retains cathode 30against ‘O’ ring 22. Cathode holder 28 can be made of flexible material,such as rubber or it could be a clamp that grips cathode 30. Cathodecoating 32 is provided with a cathode defect 36 that exposes the surfaceof cathode 30 to electrolyte 12.

Evaluator 1 further includes a conventional direct current variablepower generator 38 with DC output leads 41 that connect to anode 18 andcathode 30 such that desired DC voltages for desired durations can beapplied across anode 18, cathode 30, and electrolyte 12. Direct currentvariable power generator 38 is also in communication with a conventionalcomputer 40, such as the one supplied by Dell Computer Corporation ofRound Rock, Tex. Evaluator 1 is provided with a conventional directcurrent measurement device 42 for measuring DC voltage applied acrossanode 18, cathode 30, and electrolyte 12. Direct current measurementdevice 42 is also in communication with computer 40.

Evaluator 1 further includes a conventional alternating current variablepower generator 44 with AC output leads 46 that connect to anode 18 andcathode 30 for applying desired AC voltages at variable frequencies fordesired durations across anode 18, cathode 30, and electrolyte 12.Alternating current variable power generator 44 is also in communicationwith computer 40. Generally, AC voltage applied is about 10 to 50 mV(milliVolt), 20 to 30 mV is preferred.

Evaluator 1 further includes a conventional impedance measurement device46 with leads 48 that connect to anode 18 and cathode 30 for measuringimpedance across anode 18, cathode 30, and electrolyte 12. Impedancemeasurement device 46 is also in communication with computer 40. Thefollowing explanation provides for the basic concept utilized inimpedance measurements.

Impedance is a more general parameter that describes a circuit's abilityto resist the flow of electrical current. An electrical current can befully characterized by its amplitude and frequency characterized by acomplex function. Similarly, the impedance is usually also described asa complex function. The impedance is more general, since it also coversthe case of DC current by simply assuming the frequency (f) is zero.

The impedance (Z) of a circuit can be described by the combination ofthree ideal electrical elements, namely inductor (L), capacitor (C), andresistor (R) by the following equations:

Z(L)=j2πfL  (3)

Z(C)=−j1/(2πfC)  (4)

Z(R)=R  (5).

Where:

-   -   f is the frequency in Hz    -   L is the quantity of the inductance    -   C is the quantity of the capacitance    -   J is a symbol of complex function; √−1

It can be shown that the impedance of a resistor is independent offrequency, while the impedance of an inductor is increased as a functionof frequency and the impedance of a capacitor is inversely proportionalto the frequency. As mentioned above, in most cases, the impedance (Z)of a circuit is usually the combination of three ideal electricalelements and the actual impedance can be described by the followingcomplex function:

Z(L,C,R)=Z(L)+Z(C)+Z(R)=R+j(2πfL−1/(2πfC))=real part+j imaginarypart  (6)

Evaluator 1 further includes a computer usable storage medium 50 locatedin computer 40, which is in communication with direct current variablepower generator 38, direct current measurement device 42, alternatingcurrent variable power generator 44 and impedance measurement device 46,wherein computer readable program code means 400 (described in FIGS. 4A,4B. 4C, 4D, 4E and 4F) reside in said computer usable storage medium 50.

Computer readable program code means 400 include:

means 410 for configuring computer readable program code devices tocause computer 40 to subject said portions of anode coating 20 andcathode coating 32 to a start-up period, which can range from half anhour to one thousand hours, preferably from 3 to 15 hours.

means 412 for configuring computer readable program code devices tocause computer 40 to direct impedance measurement device 46 to measurean impedance A during said start-up period at preset intervals toproduce n1 set of said impedances A measured at preset frequenciesranging from 100000 to 10⁻⁶ Hz of AC power supplied by alternatingcurrent variable power generator 44 with an amplitude ranging from 10 to50 mV.

means 413 for configuring computer readable program code devices tocause computer 40 to generate A impedance Nyquist plot for each saidimpedance A in said n1 set as seen in FIGS. 10 and 11.

means 414 for configuring computer readable program code devices tocause computer 40 to determine start-up solution resistances(^(Sta)R_(sol.n1)) by:

-   -   1. measuring, as seen in FIG. 12, a distance between zero point        on X-axis of said A impedance Nyquist plot and a point on said        X-axis of said A impedance Nyquist plot where an impedance curve        or an extrapolated impedance curve directed to high start-up        solution frequencies in said A impedance Nyquist plot intersects        said X-axis to obtain real part of said impedance A at said high        start-up solution frequencies; and    -   2. repeating said step (1) for each said impedance A in said n1        set.

The high start-up solution frequencies can range from about 500 to about100000 Hz, preferably from about 5000 to about 10000 Hz.

means 416 for configuring computer readable program code devices tocause computer 40 to determine start-up resistances, (^(Sta)R_(Sta.n1))by:

-   -   1. measuring, as seen in FIG. 13, a distance between zero point        on X-axis of said A impedance Nyquist plot and a point on said        X-axis of said A impedance Nyquist plot where an impedance curve        or an extrapolated impedance curve directed to low start-up        resistance frequencies in said A impedance Nyquist plot        intersects said X-axis to obtain real part of said impedance A        at said low start-up resistance frequencies; and    -   2. repeating said step (1) for each said impedance A in said n1        set.

The low start-up resistance frequencies can range from about 10⁻¹ toabout 10⁻⁶ Hz, preferably from about 10⁻² to about 10⁻³ Hz.

means 418 for configuring computer readable program code devices tocause computer 40 to direct current variable power generator 38 to applyV1 preset DC voltages in a triangular, truncated triangular ortrapezoidal manner for T1 preset durations, wherein direct currentmeasurement device 42 in communication with computer 40 and connected tocathode 30 and anode 18 is used to measure said preset DC voltages andwherein the V1 preset DC voltage ranges from 0.1 millivolts to 10 volts,preferably from 0.5 volts to four volts, typically with half a voltincrements. The T1 preset duration ranges from half an hour to 100hours. The higher the DC voltage lower should be the preset duration andthe lower DC voltage higher should be the preset duration. It should beunderstood that T1 preset duration can be same for all steps or it maybe increased or decreased from step to step, if so desired. FIG. 5Aillustrates one of the typical protocols used in the process of thepresent invention, which is directed to a triangular form. FIG. 5Billustrates one of the typical protocols used in the process of thepresent invention, which is directed to a truncated triangular form.FIG. 5C illustrates one of the typical protocols used in the process ofthe present invention, which is directed to a trapezoidal form. Totaltime for performing the test can range from 2 hours to 350 hours,preferably 20 hours to 40 hours. The triangular, truncated triangular ortrapezoidal wave of DC voltages can be of a symmetrical or asymmetricalform.

means 420 for configuring computer readable program code devices tocause computer 40 to direct impedance measurement device 46 to measurean impedance B at the end of each of said preset duration at said presetfrequencies of AC power supplied by alternating current variable powergenerator 44 to produce n2 set of said impedances B.

means 421 for configuring computer readable program code devices tocause computer 40 to generate B impedance Nyquist plot for each saidimpedance B in said n2 set. These Nyquist plots would be similar tothose described earlier in FIGS. 10 through 13.

means 422 for configuring computer readable program code devices tocause computer 40 to determine triangular, truncated triangular ortrapezoidal solution resistances (^(Tra)R_(sol.n2)) by:

-   -   1. measuring a distance between zero point on X-axis of said B        impedance Nyquist plot and a point on said X-axis of said B        impedance Nyquist plot where an impedance curve or an        extrapolated impedance curve directed to high triangular,        truncated triangular or trapezoidal solution frequencies in said        B impedance Nyquist plot intersects said X-axis to obtain real        part of said impedance B at said high triangular, truncated        triangular or trapezoidal solution frequencies; and    -   2. repeating said step (1) for each said impedance B in said n2        set.

The high triangular, truncated triangular or trapezoidal solutionfrequencies can range from about 500 to about 100000 Hz, preferably fromabout 5000 to about 10000 Hz.

means 424 for configuring computer readable program code devices tocause computer 40 to determine triangular, truncated triangular ortrapezoidal resistances (^(Tra)R_(Tra.n2)) by:

-   -   1. measuring a distance between zero point on X-axis of said B        impedance Nyquist plot and a point on said X-axis of said B        impedance Nyquist plot where an impedance curve or an        extrapolated impedance curve directed to low triangular,        truncated triangular or trapezoidal resistance frequencies in        said B impedance Nyquist plot intersects said X-axis to obtain        real part of said impedance B at said low triangular, truncated        triangular or trapezoidal resistance frequencies; and    -   2. repeating said step (j) (1) for each said impedance B in said        n2 set;

The low triangular, truncated triangular or trapezoidal resistancefrequencies can range from about 10⁻¹ to about 10⁻⁶ Hz, preferably fromabout 10⁻² to about 10⁻³ Hz.

means 426 for configuring computer readable program code devices tocause computer 40 to subject the portions of anode coating 20 andcathode coating 32 to T2 preset recovery periods in between each of saidT1 preset durations. Typically, T2 preset recovery periods range fromhalf an hour to ten hours, preferably ranging from 30 minutes to 3hours. It should be understood that T2 preset recovery period can besame for all the steps or it may be increased or decreased from step tostep, if so desired.

means 428 for configuring computer readable program code devices tocause computer 40 to direct impedance measurement device 46 to measurean impedance C at the end of each of the T2 preset recovery periods atthe preset frequencies of AC power supplied by alternating currentvariable power generator 44 to produce n3 set of the impedances C.

means 429 for configuring computer readable program code devices tocause computer 40 to generate C impedance Nyquist plot for the saidimpedance C in the n3 set. These Nyquist plots would be similar to thosedescribed earlier in FIGS. 10 through 13.

means 430 for configuring computer readable program code devices tocause computer 40 to determine recovery solution resistances(^(Rec)R_(sol.n3)) by:

-   -   1. measuring a distance between zero point on X-axis of said C        impedance Nyquist plot and a point on said X-axis of said C        impedance Nyquist plot where an impedance curve or an        extrapolated impedance curve directed to high recovery solution        frequencies in said C impedance Nyquist plot intersects said        X-axis to obtain real part of said impedance C at said high        recovery solution frequencies;    -   2. repeating said step (1) for each said impedance C in said n3        set;

The high recovery solution frequencies can range from about 500 to about100000 Hz, preferably from about 5000 to about 10000 Hz.

means 432 for configuring computer readable program code devices tocause computer 40 to determine recovery resistances (^(Rec)R_(Rec.n3))by:

-   -   1. measuring a distance between zero point on X-axis of said C        impedance Nyquist plot and a point on said X-axis of said C        impedance Nyquist plot where an impedance curve or an        extrapolated impedance curve directed to low recovery resistance        frequencies in said C impedance Nyquist plot intersects said        X-axis to obtain real part of said impedance C at said low        recovery resistance frequencies; and    -   2. repeating said step (1) for each said impedance C in said n3        set;

The low recovery resistance frequencies can range from about 10⁻¹ toabout 10⁻⁶ Hz, preferably from about 10⁻² to about 10⁻³ Hz.

means 434 for configuring computer readable program code devices tocause computer 40 to calculate corrosion performance resistance(R_(perf)) of anode 18 and cathode 30 pair by using the followingequation:

R _(perf)=[Σ^(Sta) f _(n1)(^(Sta) R _(Sta.n1)−^(Sta) R_(Sol.n1))]/n1+[Σ^(Tra) f _(n2)(^(Tra) R _(Tra.n2)−^(Tra) R_(Sol.n2))]/n2+[Σ^(Rec) f _(n3)(^(Rec) R _(Rec.n3)−^(Rec) R_(Sol.n3))]/n3,

wherein n1, n2, n3 and n3 range from 1 to 100, preferably n1 ranges from5 to 15, n2 and n3 range from 3 to 10; and ^(Sta)f_(n1), ^(Tra)f_(n2),and ^(Rec)f_(n3) range from 0.0000001 to 1, preferably range from 0.1to 1. Generally, n2 is equal to n3. By way of clarification, if n1 is 5,then inside sigma (Σ), n1 in the numerator would be 1, 2, 3, 4, and 5and n1 in the denominator would be 5.

means 436 for configuring computer readable program code devices tocause computer 40 to:

-   -   (q1) direct a computer monitor to display said corrosion        performance resistance (R_(perf));    -   (q2) direct a printer to print said corrosion performance        resistance (R_(perf));    -   (q3) transfer said corrosion performance resistance (R_(perf))        to a remote computer or a remote database; or    -   (q4) a combination thereof.

FIG. 5 A illustrates one of the typical triangular DC voltage waveformprotocols used in the process of the present invention. FIG. 5 Billustrates one of the typical truncated triangular DC voltage waveformprotocols used in the process of present invention. FIG. 5 C illustratesone of the typical trapezoidal DC voltage waveform protocols used in theprocess of present invention. Total time for performing the test canrange from 2 hours to 350 hours, preferably 20 hours to 40 hours.

Preferably, direct current variable power generator 38, direct currentmeasurement device 42, alternating current variable power generator 44and impedance measurement device 46 can all be positioned in a singlestand-alone unit for convenience and ease of operation. Such a unit wasobtained from Solartron Analytical located at Farnborough, Hampshire,United Kingdom. The following website can be accessed to get furtherinformation on these devices(http://www.solartronanalytical.com/index.htm).

In order to eliminate the effect of random intrinsic defects ofcoatings, applicants made a surprising discovery that by deliberatelycreating the standardized defects of known sizes and shapes on cathodeand anode coatings and exposing the underlying anode/cathode surface toan electrolyte, the anodic dissolution of the underlying anodes and thedelamination process of the underlying cathodes can be substantiallyaccelerated in a predictable and reproducible manner when DC voltage areapplied across the cathode and anode. FIG. 6 illustrates suchdeliberately created defects 618, 620, and 622 on anode or cathodecoating 612 applied over a cathode or anode 610 that is positionedagainst chamber 614 having an ‘O’ ring 616. The most desirable defect isdefect 620, although Defect 618 is acceptable since it does expose theunderlying surface of cathode or anode 610 to the electrolyte, whereasdefect 622 is unacceptable as it does not expose the underlying surfaceof cathode or anode 610 to the electrolyte.

Preferably, anode or cathode defect, as illustrated in FIG. 7 include aplurality of circular openings 712 disposed on coating 710 that exposethe underlying surface of the anode or cathode to the electrolyte.Circular openings 712 have a diameter in the range of from 5 micrometersto 5 millimeters, 5 micrometers to 1 millimeter being preferred, eachcircular opening 712 being uniformly separated from one another by 10 to2000 times the diameter of circular openings 712. As a result, corrosioneffect illustrated by a zone 714 on one opening 712 does not spill overand affect the corrosion process on an adjacent opening 712A.Alternatively, anode or cathode coating 710 can be provided with 1 to100 of circular openings 712 per square centimeter of said cathode oranode.

Preferably, anode 18 and cathode 30 have identical shape (preferablycircular) and thickness. Preferably, anode coating 20 is identical tocathode coating 32 and preferably, anode defect 24 is identical tocathode defect 36. As a result, any deviations between the set ofcathode and anode can be eliminated.

Evaluator 1 can be provided with a thermal jacket 54 to maintain thetemperature of electrolyte 12 at a desired temperature. Typically, aheat transfer fluid 56, such as water can be used to maintain thetemperature of electrolyte 12 in the range of 0.5° C. to 99.5° C. Aconventional temperature probe 58 in communication with computer 40 canbe used to maintain the temperature of electrolyte 12 at a desiredtemperature.

Evaluator 1 can be configured to provide two or more chambers wherebyall such chambers can be maintained under similar conditions forcomparing the corrosion resistance of one set of protective coatingsagainst other, i.e., cathodes having different types of cathode coatingsapplied thereon can be compared for coating delamination performance(the lesser the delamination the better will be coating corrosionresistance properties). Similarly, anodes paired with correspondingcathodes having identical anode coatings applied thereon can be comparedfor corrosion resistance of one type of said anode coating to the othertype of said anode coating. Preferably, each paired cathode and anodewill have identical coating applied thereon. FIG. 8 illustratesmulti-chamber 800 construct whereby chambers 810 are enclosed within athermal jacket 812.

Another embodiment of the present invention 900, shown in FIG. 9,includes anode assembly 910 and cathode assembly 912 forming a leg 914of an inverted ‘Y’ (λ) to permit any gas generated in electrolyte 916during use or gas bubbles adhered on the surface of coated couponsduring installation to escape readily from a cylindrical chamber 918,which can be provided with a thermal jacket 920 containing heat transferfluid 922 having an inlet 924 and an outlet 926. Chamber 918 can befurther provided with a thermometer well 928 and a support 930.

In the alternative, applicants also contemplate another embodiment ofthe present invention wherein a chamber in the form of inverted ‘U’ (∩)with the anode and cathode positioned at the bottom of each leg of theinverted ‘∪’ shaped chamber having an opening at the apex of theinverted ‘∪’ shaped chamber to permit any gas generated in theelectrolyte during use to escape readily from the chamber.

The present invention is also directed to a process that utilizes theevaluator 1 descried in FIG. 3. The process evaluates the corrosionresistance anode coating 20 applied over a surface of anode 18 andcorrosion resistance of cathode coating 32 applied over a surface ofcathode 30 by utilizing the following steps:

(i) sealably positioning anode 18 in anode holder 16 located on chamber10 of corrosion resistance evaluator 1, chamber 10 containingelectrolyte 12 therein such that a portion of anode coating 20 isexposed to electrolyte 12, the portion of anode coating 20 having anodedefect 24 thereon;

(ii) sealably positioning cathode 30 in cathode holder 28 located onchamber 10 such that a portion of cathode coating 32 is exposed toelectrolyte 12, the portion of cathode coating 32 having cathode defect36 thereon;

(iii) directing computer 40 of evaluator 1 through computer readableprogram code means 400 (shown in FIG. 4A. 4B. 4C, 4D, 4E and 4F)residing on usable storage medium 50 located in computer 40 andconfigured to cause computer 40 to perform following steps comprising:

-   -   a. subjecting the portions of anode coating 20 and cathode        coating 30 to a start-up period;    -   b. directing impedance measurement device 46 in communication        with computer 40 and is connected to cathode 30 and anode 18 to        measure an impedance A during said start-up period at preset        intervals to produce n1 set of said impedances A measured at        preset frequencies ranging from 100000 to 10⁻⁶ Hz of AC power        with an amplitude ranging from 10 to 50 mV supplied by        alternating current variable power generator 44 in communication        with computer 40, alternating current variable power generator        44 having AC output leads 46 that connect to cathode 30 and        anode 18;    -   c. generating A impedance Nyquist plot for each said impedance A        in said n1 set;    -   d. determining start-up solution resistances (^(Sta)R_(sol.n1))        by:        -   1. measuring a distance between zero point on X-axis of said            A impedance Nyquist plot and a point on said X-axis of said            A impedance Nyquist plot where an impedance curve or an            extrapolated impedance curve directed to high start-up            solution frequencies in said A impedance Nyquist plot            intersects said X-axis to obtain real part of said impedance            A at said high start-up solution frequencies; and        -   2. repeating said step (d) (1) for each said impedance A in            said n1 set;    -   e. determining start-up resistances, (^(Sta)R_(Sta.n1)) by:        -   1. measuring a distance between zero point on X-axis of said            A impedance Nyquist plot and a point on said X-axis of said            A impedance Nyquist plot where an impedance curve or an            extrapolated impedance curve directed to low start-up            resistance frequencies in said A impedance Nyquist plot            intersects said X-axis to obtain real part of said impedance            A at said low start-up resistance frequencies; and        -   2. repeating said step (e) (1) for each said impedance A in            said n1 set;    -   f. directing direct current variable power generator 38 to apply        V1 preset DC voltages in a triangular, truncated triangular or        trapezoidal manner for T1 preset durations, wherein direct        current measurement device 42 in communication with computer 40        and connected to cathode 30 and anode 18 is used to measure said        preset DC voltages and wherein said V1 preset DC voltage ranges        from 0.1 millivolts to 10 volts and said T1 preset duration        ranges from half an hour to 100 hours;    -   g. directing impedance measurement device 46 to measure a set of        impedances B at the end of each of said preset duration at said        preset frequencies of AC power supplied by alternating current        variable power generator 44 to produce n2 said sets of said        impedances B;    -   h. generating B impedance Nyquist plot for each said impedance B        in said n2 set;    -   i. determining triangular, truncated triangular or trapezoidal        solution resistances (^(Tra)R_(sol.n2)) by:        -   1. measuring a distance between zero point on X-axis of said            B impedance Nyquist plot and a point on said X-axis of said            B impedance Nyquist plot where an impedance curve or an            extrapolated impedance curve directed to high triangular,            truncated triangular or trapezoidal solution frequencies in            said B impedance Nyquist plot intersects said X-axis to            obtain real part of said impedance B at said high            triangular, truncated triangular or trapezoidal solution            frequencies;        -   2. repeating said step (i) (1) for each said impedance B in            said n2 set;    -   j. determining triangular, truncated triangular or trapezoidal        resistances (^(Tra)R_(Tra.n2)) by:        -   1. measuring a distance between zero point on X-axis of said            B impedance Nyquist plot and a point on said X-axis of said            B impedance Nyquist plot where an impedance curve or an            extrapolated impedance curve directed to low triangular,            truncated triangular or trapezoidal resistance frequencies            in said B impedance Nyquist plot intersects said X-axis to            obtain real part of said impedance B at said low triangular,            truncated triangular or trapezoidal resistance frequencies;            and        -   2. repeating said step (j) (1) for each said impedance B in            said n2 set;    -   k. subjecting said portions of anode coating 20 and cathode        coating 32 to T2 preset recovery periods in between each of said        T1 preset durations;    -   l. directing impedance measurement device 46 to measure an        impedance C at the end of each of said T2 preset recovery        periods at said preset frequencies of AC power supplied said        alternating current variable power generator 44 to produce n3        set of said impedances C;    -   m. generating C impedance Nyquist plot for each said impedance C        in said n3 set;    -   n. determining recovery solution resistances (^(Rec)R_(sol.n3))        by:        -   1. measuring a distance between zero point on X-axis of said            C impedance Nyquist plot and a point on said X-axis of said            C impedance Nyquist plot where an impedance curve or an            extrapolated impedance curve directed to high recovery            solution frequencies in said C impedance Nyquist plot            intersects said X-axis to obtain real part of said impedance            C at said high recovery solution frequencies;        -   2. repeating said step (n) (1) for each said impedance C in            said n3 set;    -   o. determining recovery resistances (^(Rec)R_(Rec.n3)) by:        -   1. measuring a distance between zero point on X-axis of said            C impedance Nyquist plot and a point on said X-axis of said            C impedance Nyquist plot where an impedance curve or an            extrapolated impedance curve directed to low recovery            resistance frequencies in said C impedance Nyquist plot            intersects said X-axis to obtain real part of said impedance            C at said low recovery resistance frequencies; and        -   2. repeating said step (o) (1) for each said impedance C in            said n3 set;    -   p. calculating corrosion performance resistance (R_(perf)) of        said anode and said cathode pair by using the following        equation:

R _(perf)=[Σ^(Sta) f _(n1)(^(Sta) R _(Sta.n1)−^(Sta) R_(Sol.n1))]/n1+[Σ^(Tra) f _(n2)(^(Tra) R _(Tra.n2)−^(Tra) R_(Sol.n2))]/n2+[Σ^(Rec) f _(n3)(^(Rec) R _(Rec.n3)−^(Rec) R_(Sol.n3))]/n3,

-   -   wherein n1, n2, n3 and n3 range from 1 to 100; and ^(Sta)f_(n1),        ^(Tra)f_(n2), and ^(Rec)f_(n3) range from 0.0000001 to 1; and    -   q. causing computer 40 to direct a computer monitor 52 to:        -   (q1) display the corrosion performance resistance            (R_(perf)),        -   (q2) direct a printer 54 to print the corrosion performance            resistance (R_(perf)),        -   (q3) transfer the corrosion performance resistance            (R_(perf)) to a remote computer 56 or a remote database, or        -   (q4) a combination thereof.

The process of the present invention can be used comparing the corrosionresistance of one type of coating against another type of coating bytesting them under similar conditions and protocol by utilizing multiplechambers such as those shown in FIG. 8. Cathodes having different typesof cathode coatings applied thereon and said anodes having differenttypes of anode coatings applied thereon can be compared to evaluatedelamination resistance of one type of cathode coating to the other typeof cathode coating. It should be understood that each set of pairedcathode and anode would have identical coating applied thereon.Simultaneously, anodes having different types of anode coatings appliedthereon can be compared to evaluate corrosion resistance of one type ofanode coating to the other type of anode coating.

EXAMPLES Corrosion Data from the Corrosion Test Method of the PresentInvention

Eight E-coating systems designated as coating A, B, C, D, F, G, H and Iare applied on coupons and cured. On the coated surfaces of suchcoupons, six holes with a diameter of 300 microns are drilled to providestandardized anode and cathode defect, respectively. Each of the holespenetrates through the thickness of the coating and stops at theinterface of metal/coating. Standardized anode and cathode defects areidentical.

The corrosion test evaluator is based on a 26 hour test protocol thatincludes 5 sets of AC impedance measurements during 12 hours of start-upperiod (DC Volts=0), followed by four preset durations, each durationlasting two hours at triangular, truncated triangular and trapezoidalvoltages starting from 0.5 Volts, followed by 1 Volt, 2 Volts, and 3Volts. One set of AC impedance measurement is performed at the end ofeach preset duration. A 1.5 hour of recovery period is used in betweeneach preset duration. One set of AC impedance measurement is made at theend of each recovery period. The corrosion performance resistance of thecoating is calculated by using the following equation:

R _(perf)=[Σ^(Sta) f _(n1)(^(Sta) R _(Sta.n1)−^(Sta) R_(Sol.n1))]/n1+[Σ^(Tra) f _(n2)(^(Tra) R _(Tra.n2)−^(Tra) R_(Sol.n2))]/n2+[Σ^(Rec) f _(n3)(^(Rec) R _(Rec.n3)−^(Rec) R_(Sol.n3))]/n3,

wherein n1 is 5, n2 is 4, and n3 is 4 and ^(Sta)f_(n1), ^(Tra)f_(n2),and ^(Rec)f_(n3) are all equal to 1.

The foregoing ^(Sta)R_(Sta.n1), ^(Tra)R_(Tra.n2), and ^(Rec)R_(Rec.n3)are determined by the real part of the ac impedance at 10⁻² Hz from eachof the respective ac impedance measurements obtained in the respectiveperiods. ^(Sta)R_(Sol.n1), ^(Tra)R_(Sol.n2), and ^(Rec)R_(Sol.n3) aredetermined by the real part of the ac impedance at 100000 Hz from eachof the respective ac impedance measurements obtained in the respectiveperiods. The following provides further explanation of various elementused in measuring the foregoing elements:

A typical ac impedance data (for coating H) obtained by the method ofthis invention can be described in FIG. 10. The impedance data isobtained using a frequency scan from 100000 Hz to 10⁻² Hz. This plot iscalled Nyquist plot with a minus imaginary part as Y axis and a realpart as X axis. The shortcoming of this plot is that the frequency isnot explicitly expressed in the plot. Since the impedance, as notedearlier, is frequency dependent, the impedance is changed when thefrequency is changed. By the impedance data at various frequencies(normally from 100000 Hz to 10⁻² Hz), the resistance component andcapacitance component can be separated and obtained respectively. Forexample, on the far left hand of FIG. 10 which is expanded as FIG. 12, asolution resistance in the start up period, ^(Sta)R_(Sol.2), can beobtained by selecting the real part of the impedance at 100000 Hz. Onthe far right hand of FIG. 10, which is expanded as FIG. 13, a start upresistance ^(Sta)R_(Sta.2) can be obtained by selecting the real part ofthe impedance at 10⁻² Hz. The value of (^(Sta)R_(Sta.2)−^(Sta)R_(Sol.2))is also showed in FIG. 10, which can be used to calculate the corrosionresistance of the coating tested.

The accelerating factor of the method, including how fast the corrosionrate is accelerated and in what mechanisms this corrosion rate isaccelerated, is determined by the shape and duration of the DC voltagewaveforms applied in T1 preset durations. The accelerating factor can bequantified by the total amount of voltage applied in T1 preset durationsintegrated over the total time of T1 preset durations, if the otherconditions are kept the same, such as the total defected area, theconductivity of the testing electrolyte and the testing electrochemicalcell set up. For the same total duration of the testing, different DCvoltage waveforms used in T1 durations would provide differentaccelerating factors. For example, for the same total time of T1 presetdurations and the same peaks of the DC voltages, a testing protocol witha trapezoidal DC voltage waveform would have a high accelerating factorthan that of a triangular DC voltage waveform protocol. A testingprotocol with a lower accelerating factor can be selected for testing acoating system with a less corrosion protection performance, such as asingle-layer primer coating or a conversion coating. On the other hand,a higher accelerating factor testing protocol can be used for testing apremium coating system with a high corrosion protection performance,such as a multi-layer coating system. It is expected that the sameranking result can be obtained for the same group of coatings tested bydifferent test protocols with a different accelerating factors. However,the sensitivity of these test protocols with different acceleratingfactors would be different. In other words, although the absolutecorrosion resistances of the results obtained by a different testprotocol would be different, the comparative ranking of the coatingsshould be the same. Therefore, it is expected that the absolute coatingcorrosion resistances obtained in foregoing test using a triangular DCvoltage in T1 preset durations would be different from those obtainedusing a trapezoidal DC voltage, but the comparative ranking of thecoatings obtained in foregoing tests would be similar. The primarypurpose for designing a test protocol with a different acceleratorfactor, more specifically with a different DC voltage waveform used inT1 preset durations, is to provide an optimized testing sensitivity fortesting certain coating system with a different corrosion performance.

1. A process for evaluating corrosion resistance of an anode coatingapplied over a surface of an anode and corrosion resistance of a cathodecoating applied over a surface of a cathode comprising: (i) sealablypositioning said anode in an anode holder located on a chamber of acorrosion resistance evaluator, said chamber containing an electrolytetherein such that a portion of said anode coating is exposed to saidelectrolyte, said portion of said anode coating having an anode defectthereon; (ii) sealably positioning said cathode in a cathode holderlocated on said chamber such that a portion of said cathode coating isexposed to said electrolyte, said portion of said cathode coating havinga cathode defect thereon; (iii) directing a computer of said evaluatorthrough computer readable program code means residing on a usablestorage medium located in said computer and configured to cause saidcomputer to perform following steps comprising: (a) subjecting saidportions of said anode coating and said cathode coating to a start-upperiod; (b) directing an impedance measurement device in communicationwith said computer and is connected to said cathode and said anode tomeasure an impedance A during said start-up period at preset intervalsto produce n1 set of said impedances A measured at preset frequenciesranging from 100000 to 10⁻⁶ Hz of AC power with an amplitude rangingfrom 10 to 50 mV supplied by an alternating current variable powergenerator in communication with said computer, said alternating currentvariable power generator having AC output leads that connect to saidcathode and anode; (c) generating A impedance Nyquist plot for each saidimpedance A in said n1 set; (d) determining start-up solutionresistances (^(Sta)R_(sol.n1)) by:
 1. measuring a distance between zeropoint on X-axis of said A impedance Nyquist plot and a point on saidX-axis of said A impedance Nyquist plot where an impedance curve or anextrapolated impedance curve directed to high start-up solutionfrequencies in said A impedance Nyquist plot intersects said X-axis toobtain real part of said impedance A at said high start-up solutionfrequencies; and
 2. repeating said step (d) (1) for each said impedanceA in said n1 set; (e) determining start-up resistances(^(Sta)R_(Sta.n1)) by:
 1. measuring a distance between zero point onX-axis of said A impedance Nyquist plot and a point on said X-axis ofsaid A impedance Nyquist plot where an impedance curve or anextrapolated impedance curve directed to low start-up resistancefrequencies in said A impedance Nyquist plot intersects said X-axis toobtain real part of said impedance A at said low start-up resistancefrequencies; and
 2. repeating said step (e) (1) for each said impedanceA in said n1 set; (f) directing a direct current variable powergenerator to apply V1 preset DC voltages in a triangular, truncatedtriangular or trapezoidal manner for T1 preset durations, wherein saiddirect current measurement device in communication with said computerand connected to said cathode and said anode is used to measure saidpreset DC voltages and wherein said V1 preset DC voltage ranges from 0.1millivolts to 10 volts and said T1 preset duration ranges from half anhour to 100 hours; (g) directing said impedance measurement device tomeasure an impedance B at the end of each of said preset duration atsaid preset frequencies of AC power supplied by said alternating currentvariable power generator to produce n2 set of said impedances B; (h)generating B impedance Nyquist plot for each said impedance B in said n2set; (i) determining triangular, truncated triangular or trapezoidalsolution resistances (^(Tra)R_(sol.n2)) by:
 1. measuring a distancebetween zero point on X-axis of said B impedance Nyquist plot and apoint on said X-axis of said B impedance Nyquist plot where an impedancecurve or an extrapolated impedance curve directed to high triangular,truncated triangular or trapezoidal solution frequencies in said Bimpedance Nyquist plot intersects said X-axis to obtain real part ofsaid impedance B at said high triangular, truncated triangular ortrapezoidal solution frequencies;
 2. repeating said step (i) (1) foreach said impedance B in said n2 set; (j) determining triangular,truncated triangular or trapezoidal resistances (^(Tra)R_(Tra.n2))by:
 1. measuring a distance between zero point on X-axis of said Bimpedance Nyquist plot and a point on said X-axis of said B impedanceNyquist plot where an impedance curve or an extrapolated impedance curvedirected to low triangular, truncated triangular or trapezoidalresistance frequencies in said B impedance Nyquist plot intersects saidX-axis to obtain real part of said impedance B at said low triangular,truncated triangular or trapezoidal resistance frequencies; and 2.repeating said step (j) (1) for each said impedance B in said n2 set;(k) subjecting said portions of said anode coating and said cathodecoating to T2 preset recovery periods in between each of said T1 presetdurations; (l) directing said impedance measurement device to measure animpedance C at the end of each of said T2 preset recovery periods atsaid preset frequencies of AC power supplied by said alternating currentvariable power generator to produce n3 set of said impedances C; (m)generating C impedance Nyquist plot for each said impedance C in said n3set; (n) determining recovery solution resistances (^(Rec)R_(sol.n3))by:
 1. measuring a distance between zero point on X-axis of said Cimpedance Nyquist plot and a point on said X-axis of said C impedanceNyquist plot where an impedance curve or an extrapolated impedance curvedirected to high recovery solution frequencies in said C impedanceNyquist plot intersects said X-axis to obtain real part of saidimpedance C at said high recovery solution frequencies;
 2. repeatingsaid step (n) (1) for each said impedance C in said n3 set; (o)determining recovery resistances (^(Rec)R_(Rec.n3)) by:
 1. measuring adistance between zero point on X-axis of said C impedance Nyquist plotand a point on said X-axis of said C impedance Nyquist plot where animpedance curve or an extrapolated impedance curve directed to lowrecovery resistance frequencies in said C impedance Nyquist plotintersects said X-axis to obtain real part of said impedance C at saidlow recovery resistance frequencies; and
 2. repeating said step (o) (1)for each said impedance C in said n3 set; (p) calculating corrosionperformance resistance (R_(perf)) of said anode and said cathode pair byusing the following equation:R _(perf)=[Σ^(Sta) f _(n1)(^(Sta) R _(Sta.n1)−^(Sta) R_(Sol.n1))]/n1+[Σ^(Tra) f _(n2)(^(Tra) R _(Tra.n2)−^(Tra) R_(Sol.n2))]/n2+[Σ^(Rec) f _(n3)(^(Rec) R _(Rec.n3)−^(Rec) R_(Sol.n3))]/n3, wherein n1, n2, n3 and n3 range from 1 to 100; and^(Sta)f_(n1), ^(Tra)f_(n2), and ^(Rec)f_(n3) range from 0.0000001 to 1;and (q) causing said computer to: (q1) direct a computer monitor todisplay said corrosion performance resistance (R_(perf)); (q2) direct aprinter to print said corrosion performance resistance (R_(perf)); (q3)transfer said corrosion performance resistance (R_(perf)) to a remotecomputer or a remote database; or (q4) a combination thereof.
 2. Theprocess of claim 1 wherein said cathode and said anode are made ofsteel.
 3. The process of claim 1 wherein said anode coating and saidcathode coating results from a multilayer coating composition comprisingan automotive OEM paint, an automotive refinish paint, a marine paint,an aircraft paint, an architectural paint, an industrial paint, arubberized coating, a polytetrafluoroethylene coating, or a zinc-richprimer.
 4. The process of claim 1 wherein said chamber is surrounded bya thermal jacket to maintain temperature of said electrolyte at adesired temperature ranging from 0.5° C. to 99.5° C.
 5. The process ofclaim 1 wherein two or more of said chambers are surrounded by a thermaljacket to maintain temperature of said electrolyte in each of saidchambers at a desired temperature ranging from 0.5° C. to 99.5° C. 6.The process of claim 1 wherein said anode coating is identical to saidcathode coating.
 7. The process of claim 1 wherein said anode defect isidentical to said cathode defect.
 8. The process of claim 1 wherein saidanode defect comprises a plurality of circular openings disposed on saidcoating that expose said underlying surface of said anode to saidelectrolyte.
 9. The process of claim 1 wherein said cathode defectcomprises a plurality of circular openings disposed on said coating thatexpose said underlying surface of said cathode to said electrolyte. 10.The process of claim 9 wherein said cathode or anode defect comprisescircular openings each having a diameter in the range of from 5micrometers to 3 millimeters, each said circular opening being uniformlyseparated from one another by 10 to 1000 times the diameter of saidcircular openings.
 11. The process of claim 10 wherein said cathode oranode defect comprises in the range of from 1 to 100 of said circularopenings per square centimeter of said cathode or anode, said circularopening being uniformly separated from one another, and wherein saidcircular opening has a diameter in the range of from 5 micrometers to 5millimeters, each said circular opening being uniformly separated fromone another by 10 to 2000 times the diameter of said circular openings.12. The process of claim 10 wherein said cathode or anode defectcomprises in the range of from 1 to 100 of said circular openings persquare centimeter of said cathode or anode, said circular opening beinguniformly separated from one another, and wherein said circular openinghas a diameter in the range of from 5 micrometers to 5 millimeters. 13.The process of claim 1 wherein said electrolyte comprises: (a) anaqueous solution containing sodium chloride at a concentration of 3parts by weight based on 100 parts by weight of said aqueous solution,(b) an aqueous solution that simulates acid rain, or (c) a corrosivechemical solution.
 14. The process of claim 1 wherein said anode holderand said cathode holder each form a leg of an inverted ‘Y’ to permit anygas generated during use or gas bubbles adhered on the surface of coatedcoupons during installation to escape readily from said chamber.
 15. Theprocess of claim 1 wherein said anode holder and said cathode holder arepositioned at the opposite ends of said chamber to permit any gasgenerated during use to escape readily from said chamber.
 16. Theprocess of claim 1 wherein said start-up period ranges from half an hourto one thousand hours.
 17. The corrosion resistance evaluator of claim 1wherein said preset interval ranges from half an hour to ten hours.